Whew. I followed the advice of others on here, I simply asked my father if he knew about his open mouth eating and if he could stop. I was fearing this moment for months, since I assumed my mom already instructed him not to do so.
Earlier he was eating a slice of pizza with his mouth wide open and loud right in front of me while talking to me. I thought to myself it was enough, I had to talk to him. I felt like the moment was right.
I entered his bedroom and told him I had to talk to him about something that had been on my mind for a long time. He said that I could ask him what I wanted to.
I asked him if he had any idea that he opens his mouth when he eats. He said he had no idea.
He told me to just tell him next time I catch him and he said it would be no big deal. He said that he just didn't realize what he was doing. Wow!! I thought my mom told him not to, that's what she said. But he said he doesn't remember her mentioning that.
You guys where correct, just had to ask him! Of course he ate with his mouth open when no one every told him not to!